In a cellular phone terminal and a cellular phone network using the third-generation W-CDMA technique, a circuit switching network or a circuit switching protocol is used in order to realize a voice telephone and a TV telephone.
In the meantime, there is a trend toward providing multimedia service on such a circuit switching network by using an IMS on an IP network. In the future, various services are going to be integrated on an IMS core network. The configuration of an IMS is described in, for example, non-patent document 1, which is described below and TS23.228 specified by 3GPP (3rd Generation Partnership Project).